The technical field of the invention relates to bicycles and other humanly powered vehicles and, more specifically, to automatic and hybrid transmission systems for humanly powered vehicles, herein generically referred to as xe2x80x9cbicyclesxe2x80x9d.
Forty years ago the automatic transmission for automobiles was for many people what the electric automobile engine starter had been for an earlier generation. Yet, even though bicycles and the like have been around for as long as the automobile, velocipedists all over the world still do not have automatic transmissions that would actually benefit them on their humanly powered vehicles.
Various proposals for automatic bicycle transmissions have not been widely successful. One recent proposal adds three weights, 120 degrees apart, to the rear wheel. These weights add increased air resistance and more than a kilogram of mass to the bicycle. Also, these weights respond to rear wheel speed by centrifugal or centripetal action, shifting a derailleur transmission automatically. In practice, shifting a transmission or derailleurs in response to speed has its disadvantages. Consider for instance approaching an upgrade with a bicycle. In such a case, the cyclist would pedal harder; his or her reaction being to maintain the speed. This, of course, would delay the necessary shifting of the transmission until the hard pedaling cyclist can no longer maintain the speed. By thus losing speed, the cyclist in effect has to work harder in taking the hill, even after the transmission has shifted. Conversely, going downhill and onto a level surface may be hard on the brakes, since that transmission will not shift back until the speed has gone down.
Velocipedists thus continue to shift their bicycles manually in response to the load on their legs and feet. This has led to a continual increase in the number of gears or transmission shift positions with which bicycle transmissions are manufactured, especially for mountainous driving. A high number of transmission shift positions, in turn, is requiring increasing sophistication of bicycle riders as to how and when to shift, and has been discouraging many people from acquiring one of the more advanced racing bicycles or xe2x80x9cmountain bikesxe2x80x9d.
The problem may be gauged from a commercial eight-speed version in which the speed change or change in drive ratio is 22% from the first to the second gear, 15% from the second to the third gear, 18% from the third to the fourth gear, 21% from the fourth to the fifth gear, 20% from the fifth to the sixth gear, 17% from the sixth to the seventh gear, and 22% from the seventh to the eighth gear. That the problem has assumed grotesque proportions may be seen from the example of a modern eighteen-speed derailleur-type bicycle having front sprocket control cam followers and rear sprocket control cam followers providing together the following plethora of drive ratio changes: 22% from the first to the second; 11% from the second to the third; 3% from the third to the fourth; 18% from the fourth to the fifth; nothing from the fifth to the sixth, due to the combined action of the front sprocket and rear sprocket shifts; 4% each between the sixth and the seventh, the tenth and the eleventh, and the fifteenth and the sixteenth; 9% between the seventh and the eight; 2% between the eight and the ninth; 5% between the ninth and the tenth; 7% between the eleventh and the twelfth, the twelfth and the thirteenth, the fourteenth and the fifteenth, and the seventeenth and the eighteenth; with only 6% between the thirteenth and the fourteenth; and 13% between the sixteenth and the seventeenth.
This averages out as a ratio change of 0.07166 per shift of that 18-speed transmission, with actual values being very unequally distributed among the eighteen shift positions. In consequence, more sophistication, concentration and judgment are required for operating the transmission, that what is needed to conduct the,bicycle itself.
Known hub type of bicycle transmissions work with one or two planetary gear systems, but are not automatic.
Further problems arise from the fact that recurring torque variations are inherent in many humanly powered drives, such as in bicycles where twice-around drops in torque occur from the fact that the angularly moved pedals in turn have to go through tops and bottoms of their circular motions. This, in turn, has beset efforts to develop an automatic bicycle transmission with problems of erratic shifting due mainly to the above mentioned cyclically recurring power torque variations.
In consequence, a newer approach thus uses a microprocessor for shifting gears which, however, harks back to the power-assisted manual type of transmission of the old Hudson automobile, circa 1938. A new approach obviously is needed, even in the case of electromechanical solutions.
The prior-art inability to evolve a widely acceptable automatic bicycle transmission is regrettable also from environmental and socio-economic points of view, since bicycles cost much less and take much less space than automobiles, put less of a load on the road, do not pollute the atmosphere like automobiles, are much less expensive to operate, and subject the rider to continual salubrious exercise unavailable in any automobile.
The primary object of the invention is to provide improved automatic bicycle transmission systems.
The invention resides in a method of shifting a shiftable bicycle transmission, comprising, in combination, automatically sensing output power torque of the transmission, automatically converting sensed output power torque to transmission shifting motion, and automatically shifting the shiftable transmission with that transmission shifting motion.
The invention resides also in a shiftable bicycle driving power transmission having a transmission shifting element, comprising, in combination, a bicycle output power torque sensor, and an output power torque-to-transmission shifting motion converter having an output power torque input coupled to that output power torque sensor and having a transmission shifting motion output, such transmission shifting element being coupled to the transmission shifting motion output of the converter.